Conventionally, there has been known a valve timing controller that includes: a housing for receiving the driving force of the crankshaft of an engine; and a vane rotor received in the housing and transferring the driving force of the crankshaft to a camshaft, and that turns the vane rotor toward a retard side and an advance side with respect to the housing by a working fluid pressure in a retard hydraulic chamber and an advance hydraulic chamber to adjust the phase of the camshaft to the crankshaft, that is, a valve timing.
In the valve timing controller like this, torque variation that the intake valve or the exhaust valve receives from the camshaft when the intake valve or the exhaust valve is opened or closed is transferred to the vane rotor, whereby the vane rotor receives the torque variation on a retard side or an advance side with respect to the housing. When the vane rotor receives the torque variation on the retard side, the working fluid in the advance hydraulic chamber receives force to flow out of the retard hydraulic chamber and when the vane rotor receives the torque variation on the advance side, the working fluid in the retard hydraulic chamber receives force to flow out of the retard hydraulic chamber. Then, there is presented the following problem: for example, when the pressure of the working fluid supplied from a fluid supply source is low, in a case where the working fluid is supplied to the advance hydraulic chamber to change the phase of the camshaft from the retard side to the advance side with respect to the crankshaft, as shown by a dotted line in FIG. 23, the vane rotor is returned to the retard side by the torque variation to elongate a response time that elapses before a target phase is reached.
As described in JP 2003-106115A, it is thought that a check valve is disposed in a supply passage for supplying a working fluid to a retard hydraulic chamber and an advance hydraulic chamber to prevent the working fluid from flowing out of the retard hydraulic chamber or the advance hydraulic chamber even if a vane rotor receives torque variation. It is known in this manner that, as shown in FIG. 23, the vane rotor is prevented from returning to the opposite side of a target phase with respect to a housing during performing a phase control to enhance the responsivity of the phase control.
However, check valves are disposed in a retard supply passage and an advance supply passage that supply the working fluid to the retard hydraulic chamber and the advance hydraulic chamber, respectively, which in turn presents a problem of increasing the number of parts.
Meanwhile, torque variation that a camshaft receives from an intake valve or an exhaust valve when the intake valve or the exhaust valve is opened or closed is applied on the average in a direction that prevents the rotation of the camshaft, in other words, on the retard side (hereafter, direction of torque variation applying on the retard side is referred to as “positive” and direction of torque variation applying on the advance side is referred to as “negative”), so that even in a construction having a check valve not disposed in the retard supply passage, a valve timing can be controlled on the retard side within a comparatively short response time.
Hence, U.S. Pat. No. 5,657,725 discloses an apparatus having a check valve disposed only in an advance supply passage. Moreover, there is disclosed the following passage construction: in the case of performing the advance control of valve timing, even when torque variation is applied on the retard side, the check valve prohibits the working fluid from flowing out of the advance hydraulic chamber and when torque variation is applied on the advance side, the working fluid flowing out of the retard hydraulic chamber flows into the advance hydraulic chamber. In this manner, in the case of performing the advance control, the working fluid flowing out of the retard hydraulic chamber is supplied to the advance hydraulic chamber by the use of torque variation applied on the retard side to assist the advance control of valve timing.
However, according to the apparatus disclosed in U.S. Pat. No. 5,657,725 (FIG. 3A to FIG. 3C), a check valve is disposed only in the advance supply passage, it is only one retard hydraulic chamber and one advance hydraulic chamber that have the working fluid supplied from a fluid supply source. As a result, in the construction in which the advance control of valve timing is performed by the use of torque variation that the camshaft receives on the retard side, as shown in FIGS. 24A and 24B, when the cylinders increases in number to reduce torque variation applied to the camshaft on the retard side, in a case where the number of revolutions of the engine is small and where the pressure of the working fluid is low, there is a possibility that the responsivity of the phase control to the advance side will deteriorate or that the phase control to the advance side will not be performed. FIG. 24A is an example showing the torque variation of an in-line 4-cylinder engine and FIG. 24B is an example showing the torque variation of an in-line 6-cylinder engine.